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The clearest trend in the Tropical Andes is the increase
in air temperature. The Tropical Andes are expected
to experience some of the most drastic change in
climate in South America (Urrutia and Vuille, 2009;
Hijmans et al., 2005). However, projections of future
climate change using different models in the Tropical
Andes are highly uncertain, particularly for rainfall.
For temperature there is a higher degree of agreement
between the different models. This is partly because
the topography of the region is too rugged to be
captured by low-resolution global models. In addition,
there is not a high density of meteorological stations,
which would be needed for validating and calibrating
climate models. Climate models, therefore, differ
more from observations in the Andes than in other
parts of South America. This is true for both models
on temperature and precipitation projections. While
especially in short-termprojections internal variability
(“noise”) of the modelled processes is often larger than
any trends, for longer time scales the signal-to-noise
ratio improves and allows for deriving robust trends
(in particular for temperature).
El Niño and la Niña events have strong, though
varying, effects on both precipitation and temperature
in South America and the Tropical Andes. The overall
frequency of El Niño events is expected to decrease
slightly. Extreme El Niño events, however, are in
recent studies predicted to increase in frequency due
to global warming (Cai et al., 2014). El Niño events
are also associated with extremely warm years,
thereby adding to the predicted warming.
Temperature
Future warming is predicted to be highest in the
mountains (Urrutia and Vuille, 2009; Bradley et al.,
Projections
2004). In all medium emission scenarios, by 2100
the coldest years in the Tropical Andes Mountains
will be significantly warmer than the warmest years
people have adapted to over the centuries (Vuille,
2013). This means that by 2100, temperatures will
be unprecedented for current social and ecological
systems. It is important to remember that climate
variability, such as by ENSO events, will also affect
how climate change manifests at particular times in
the future.
In a high-emission scenario (RCP8.5), temperatures
in the Tropical Andes are expected to increase by
4.5-5°C by 2100 (Bradley et al., 2009; Hijmans et al.,
2005). It should be noted that models vary greatly in
their projections for the regions, and are particularly
uncertain in mountain regions, but all models agree
that temperature will increase (Valdivia et al., 2010).
In some models, the Bolivian Altiplano is expected
to experience 3-4°C warming (Anderson et al., 2011,
Minvielle and Garreaud, 2011). A high-resolution
model projects significantly greater warming at
higher altitudes, from 3.5°C warming at 500 m
to 4.8°C warming above 4,000 m on the western
slopes (Urrutia and Vuille, 2009). In low emission
scenarios, the expected warming has about half the
amplitude. Available models also project a higher
frequency of warming than today’s average in the
years approaching 2100.
Precipitation
Most studies on precipitation focus on changes in
total annual precipitation. However, for the Tropical
Andes the main change may be in seasonal variability.
In southern Peru and Bolivia, for instance, climate
models predict more intense and concentrated rainy
seasons and longer dry seasons (Seth et al., 2010).
However, it is important to recognize the high
variance of precipitation patterns within these areas.
The expected changes in total annual precipitation
are generally low and uncertain in South America
as a whole. However, models predict that in a high-
emission scenario there will be significant changes
for some sub-areas (Magrin et al., 2014). In general,
wet areas will get wetter, and dry areas will mostly
get drier. The north-western Andes of Colombia,
Ecuador and Peru will experience increased rainfall,
while a decrease is expected in the north-eastern
Andes of Venezuela and Columbia, in southern Peru
and in the Bolivian mountains (Vuille et al., 2008;
Magrin et al., 2014; Hijmans et al., 2005).
Girl, Peru